Large tunnels for subways, mining and highway are made with tunnel boring equipment. A typical tunnel boring machine includes a large diameter cutter head of a diameter only slightly less than the diameter of a tunnel being bored. The head is rotatively mounted on a machine body which in turn is mounted on wheels for advance as the head is rotated. Conveyors behind the head transport cuttings rearwardly for removal from the tunnel.
The cutter head carries a plurality of cutters. In the past such cutters have been fixedly and coaxially mounted on hubs for rotation about the hub and cutter axis. Cutter rotation is caused by frictional engagement of each cutter with the head wall as the boring head is advanced and rotated.
Boring a tunnel is a very slow and time consuming procedure. Accordingly it would be desirable to provide improved cutters which would reduce the time consumed in boring a tunnel.